title: Evidence of apothecial ancestry in the cleistothecial ascomata of Pleuroascus nicholsonii.
abstract: Ascomata of Pleuroascus nicholsonii, a rarely reported cleistothecial ascomycete, show little overt evidence of a putative affiliation with the Leotiomycetes. However, close examination of the plectomycetous centrum reveals a distorted hymenium arising from a system of branched ascogenous hyphae, and twisted or coiled uniseriate ascospores enclosed within what appears to be the remains of the spore investing membrane of a clavate ascus precursor. Abundant sterile elements arising from the inner wall layer of the peridium and interspersed throughout the centrum are interpreted as representing vestiges of apically branched paraphyses. Whole ascomata show limited signs of polarity, although the characteristic, tightly coiled appendages generally arise along or below the equatorial region and there is a marked thinning of subicular hyphae over the crown of the cleistothecium. The mature peridium, which consists of a thin, melanized outer layer of squamulose cells, splits irregularly along intercellular grooves when disturbed. The adaptive significance of these characteristics is unknown, but the persistent paraphyses, the easily fractured and darkly pigmented membranous peridium, an ascospore mass that is dry at maturity, and the tendency for ascomata to cling together in clumps can be rationalized in the context of a coprophilous life-style. Collection data for P. nicholsonii provide further support for this supposition because five of the six reported specimens are from rodent dung.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Marcie J R
authors.initials: MJ
authors.lastname: Plishka
authors.forename: Akihiko
authors.initials: A
authors.lastname: Tsuneda
authors.forename: Randolph S
authors.initials: RS
authors.lastname: Currah
mesh_terms: D001203:Ascomycota / Q000648:ultrastructure*; D005075:Biological Evolution; D025301:Hyphae / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D013172:Spores, Fungal / Q000648:ultrastructure*